1. Field of the Invention
The present invention relates to a synchronous recording system and a synchronous recording method.
2. Description of Related Art
A related art recording apparatus, e.g., seismograph, has a function to perform time calibration through use of a global positioning system (GPS), as generally discussed in Japanese Patent Laid Open Application No. 2001-215283, for example. In addition, a related art system connects a plurality of such recording apparatuses in order to effectively perform measurement at a plurality of locations.
In such a system connecting a plurality of recording apparatuses, all of the apparatuses used are normally time-calibrated through use of a GPS or a time announcement signal. This is because, without internal clocks in the apparatuses being synchronized with the absolute time, the difference between the absolute time and the internal clocks becomes larger as the time goes by, and it becomes necessary to calibrate the internal clocks and to correct times after collecting the measured data. Further, all of the recording apparatuses after time calibration are synchronized for recording, by directly connecting the apparatuses using the synchronization signal of hardware.
However, with the above-described related art synchronization method, the synchronization signal which connects two recoding apparatuses A and B, for example, is a hardware signal, thereby having a limitation in distance for connecting the two recording apparatuses A and B and susceptible to external disturbances such as noise in the transmission path. Further, in the above-described synchronization method, it is difficult to have a perfect synchronization. In particular, as shown in FIG. 6, since there is a delay in the transmission path where the synchronization signal is transmitted from the recording apparatus A to the recording apparatus B, or a delay in processing at the reception side, a difference is caused between recording initiation location Tb of the recording apparatus B and recording initiation location Ta of the recording apparatus A, i.e., ΔT=Tb−Ta. In other words, the synchronization is performed only from recording from the time of receiving the synchronization signal, thereby causing a limitation in time.